The invention relates generally to the manufacture of medical devices and, more particularly, to an apparatus and a method for modifying a surface of a medical device designed for use or implantation within the body of a patient.
In the semiconductor, industrial, electronics, and aerospace fields, conventional plasmas and plasma chambers implant, deposit, and/or mix various compounds and materials onto or into a surface or surfaces of planar targets such as silicon wafers, machine tools, or machine parts. These plasma coatings improve coefficients of friction, clean surfaces of various objects, and improve resistance to wear and corrosion.
In the biomedical field, ionized plasmas are used to harden housings of artificial joints and to manufacture intra-luminal devices such as stents and catheters. However, non-uniform implantation or deposition of atomic species associated with the cylindrical nature of intra-luminal devices creates problems. Surface defects, voids, and roughness, as well as leaching of chemicals can result from non-uniform implantation or deposition processes. Variations in a medical device""s surface structure, such as bumps, trenches, or raw edges, can create potentially life-threatening situations by wearing or damaging the interior surfaces of vessels or vital organs. Wear or damage to vessels or vital organs can cause adhesions, influx of inflammatory cells, or overgrowth of tissue resulting in strictures, blockages, and restenosis, the narrowing of blood vessels. Non-uniform surfaces can cause proliferation of bacteria, formation of blood clots, disruption of blood flow, and/or calcification deposits. Leaching chemicals may cause toxic side effects or allergic reactions. Similarly, flaking or breakage resulting from non-uniform implantation may result in the deposition of potentially toxic materials throughout the body. For these reasons, it is desirable to manufacture implantable medical devices having biocompatible, chemically stable, and uniformly deposited surfaces.
Plasma ion implantation is preferred over conventional implantation methods because it provides a uniform ion dose and avoids many of the problems associated with shadowing and excessive sputtering. Of particular relevance to the biomedical field, plasma ion implantation has been shown to provide uniform doses of atom species on nonplanar targets without the necessity of manipulating those targets within the plasma chamber. Moreover, plasma ion implantation is desirable for use in medical applications because the implanted materials do not leach out, wash off, or become part of the blood stream.
Problems common in the art include non-uniform deposition or implantation of ions, especially where three dimensional target objects are concerned, and arcing, a luminous discharge of current typically associated with high voltages that can damage target objects.
The present invention provides a cylindrical plasma reaction chamber in which a cylindrical screen is coaxially positioned about a target. Concurrently biasing the screen and target with separate negative voltages not only increases the plasma density near the target area, resulting in a uniform deposition or implantation of ions, but also lessens the dangers associated with arcing, a luminous discharge of current typically associated with high voltages. Moreover, the cylindrical nature of the plasma reaction chamber and the screen allow uniform implantation of three-dimensional target objects.
A plasma ion surface modification apparatus is disclosed. The plasma ion surface modification apparatus includes a reaction vessel that has a base and a reaction chamber. An electrode is centrally positioned on the base within the chamber. A perforated grid is located within the chamber. The perforated grid encloses a target zone, and is coupled to a voltage source.